1. Field of the Invention
This invention relates to novel 5H-dibenzo[a,d] cycloheptanylidene derivatives and 5H-dibenzy[a,d]cycloheptenylidene derivatives, a process for producing the same and an electrophotographic photosensitive member using the same.
2. Related Background Art
Heretofore, inorganic photoconductive materials such as selenium, zinc oxide, cadmium sulfide, etc. have been widely used in the electrophotographic photosensitive layer, and recently research for using organic photoconductive materials as an electrophotographic photosensitive member have been extensively made.
Basic characteristics required for the electrophotographic photosensitive member are 1) a good chargeability up to an appropriate potential in a dark place by corona discharge, etc., 2) a good charge retention in a dark place, 3) a rapid potential dischargeability by light irradiation, 4) less residual potential after the light irradiation, etc.
Electrophotographic photosensitive members using the conventional inorganic electroconductive materials such as selenium, zinc oxide, cadmium sulfide, etc. have the said basic characteristics to some extent, but still have such production problems as difficult film formability, poor flexibility, a high production cost, etc. Furthermore, inorganic photoconductive materials generally have a high toxicity, and thus it is desirable from this point of view to use an organic photosensitive member in place of the inorganic photosensitive member. Generally, organic materials have such advantages as light weight, good film formability and flexibility, low production cost, low toxicity, etc., as compared with inorganic materials.
Thus, recent research for electrophotographic photoconductive materials using organic materials, have been extensively made, and many electrophotographic photosensitive members have been proposed and practically used.
Various organic photoconductive polymers including poly-N-vinylcarbazole as a typical organic electrophotographic photosensitive material have been so far proposed, and are better in the weight, film formability, etc., than inorganic photoconductive materials, but are poorer in the sensitivity, durability, stability against changes in surrounding atmosphere, mechanical strength, etc., than the inorganic photoconductive materials and thus are practically less used.
Low molecular weight, organic photoconductive materials such as hydrozone compounds disclosed in U.S. Pat. No. 4,150,987, triarylpyrazoline compounds disclosed in U.S. Pat. No. 3,837,851, and 9-styrylanthracene compounds disclosed in Japanese Patent Publications Kokai (Laid-open) Nos. 94828/1976 and 94829/1976, etc. have been proposed. These low molecular weight, organic photoconductive materials can overcome the disadvantage of poor film formability as a problem in the field of organic photoconductive polymers by properly selecting a binder to be used, but still are not satisfactory in their sensitivity.
Recently, a laminated structure type, in which the photosensitive layer is functionally divided into a charge generation layer and a charge transport layer, has been proposed. An electrophotographic photosensitive member using a photosensitive layer of such a laminated structure type has improvements in the sensitivity to visible light, charge retention, surface strength, etc. Such electrophotographic photosensitive members as above are disclosed, for example, in U.S. Pat. Nos. 3,837,851, 3,871,882 and 4,245,021; British Patent No. 2,121,789 [Japanese Patent Application Kokai (Laid-open) No. 198043/1976], Japanese Patent Application Kokai (Laid-open) No. 161247/1980, etc.
However, the electrophotographic photosensitive members using the conventional low molecular weight, organic photoconductive material in the charge transport layer are not always satisfactory in sensitivity and characteristics, and have a large fluctuation in the light portion potential and the dark portion potential when subjected to repeated charging and light exposure and thus still have points to be improved.
As a result of extensive studies of organic photoconductive materials for electrophotographic photosensitive members, the present inventors have synthesized novel 5H-dibenzo[a,d]cycloheptanylidene derivatives and 5H-dibenzo[a,d]cycloheptenylidene derivatives, each having a 7-membered ring structure, and have found that these compounds are very useful as the organic photoconductive materials.